Described is a broadly based research program that seeks to understand normal brain function by studying the mechanisms underlying species-typical behaviors. This goal is relevant to mental health since information on the control of normal behavior provides the context in which to determine and evaluate psychopathology. The approach used is both comparative and multidisciplinary. The comparative method provides model systems with which to understand the evolutionary rules which govern a behavior as well as its roots. Multidisciplinary studies spanning the molecular to the population levels of biological organization reveal a multifaceted, yet integrated, perspective behavior. The proposed experiments focus on two fundamental aspects of the biological control of reproductive and agonistic behavior. The first question concerns the role of pheromones, species-typical chemical signals, in the control of behavior. A long-standing research program on pheromones has utilized the red-sided garter snake as a model system to better understand the relationship among pheromones, hormones, and behavior. This animal depends completely on pheromones to coordinate reproduction between the male and the female. The second question concerns the evolution of the cellular responses to hormones activating gender-typical mating behaviors. Advantage is taken of the fact that unisexual (parthenogenetic) whiptail lizards are known to have directly descended from extant sexual gonochoristic species, thereby allowing direct ancestor- descendant comparisons. Further, by their nature of reproduction, animals simultaneously remove two of the greatest confounds in sex differences research: genetic variation and gender. The studies proposed employ behavioral observation in the field and in the laboratory, intracranial implantation, 2-deoxyglucose utilization, hormone-receptor analysis, radioimmunoassay, and mass spectra, thin-layer and gas chromatographic analyses.